A Japanese Patent Application First Publication (tokkai) 2007-244058 published on Sep. 20, 2007 exemplifies a previously proposed capacity adjustment system which performs capacity adjustments between a plurality of battery cells constituting an assembled battery. In such a previously proposed capacity adjustment system as described above, a difference in a consumed current between a plurality of current consumption devices, each current consumption device operated with a voltage of a particular battery cell as a voltage source, is calculated in accordance with a presence or absence of a photo-coupler constituting a corresponding one of the current consumption devices and one or more of the cells are discharged to adjust the capacity of the corresponding one or more of the cells on a basis of the difference in the consumed current described above.